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.\" ========================================================================
.\"
.IX Title "Catmandu::Store::DBI::Bag 3pm"
.TH Catmandu::Store::DBI::Bag 3pm "2023-02-02" "perl v5.36.0" "User Contributed Perl Documentation"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
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.nh
.SH "NAME"
Catmandu::Store::DBI::Bag \- implementation of a Catmandu::Bag for DBI
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 10
\&    my $store = Catmandu::Store::DBI\->new(
\&        data_source => "dbi:SQLite:dbname=/tmp/test.db",
\&        bags => {
\&            data => {
\&                mapping => {
\&                    _id => {
\&                        column => \*(Aqid\*(Aq,
\&                        type => \*(Aqstring\*(Aq,
\&                        index => 1,
\&                        unique => 1
\&                    },
\&                    author => {
\&                        type => \*(Aqstring\*(Aq
\&                    },
\&                    subject => {
\&                        type => \*(Aqstring\*(Aq,
\&                    },
\&                    _data => {
\&                        column => \*(Aqdata\*(Aq,
\&                        type => \*(Aqbinary\*(Aq,
\&                        serialize => \*(Aqall\*(Aq
\&                    }
\&                }
\&            }
\&        }
\&    );
\&
\&    my $bag = $store\->bag(\*(Aqdata\*(Aq);
\&
\&    #SELECT
\&    {
\&        #SELECT * FROM DATA WHERE author = \*(AqNicolas\*(Aq
\&        my $iterator = $bag\->select( author => \*(AqNicolas\*(Aq );
\&    }
\&    #CHAINED SELECT
\&    {
\&        #SELECT * FROM DATA WHERE author = \*(AqNicolas\*(Aq AND subject = \*(AqICT\*(Aq
\&        my $iterator = $bag\->select( author => \*(AqNicolas\*(Aq )\->select( subject => \*(AqICT\*(Aq );
\&    }
\&    #COUNT
\&    {
\&        #SELECT * FROM DATA WHERE author = \*(AqNicolas\*(Aq
\&        my $iterator = $bag\->select( author => \*(AqNicolas\*(Aq );
\&
\&        #SELECT COUNT(*) FROM ( SELECT * FROM DATA WHERE author = \*(AqNicolas\*(Aq )
\&        my $count = $iterator\->count();
\&    }
\&    #DETECT
\&    {
\&        #SELECT * FROM DATA WHERE author = \*(AqNicolas\*(Aq AND subject = \*(AqICT\*(Aq LIMIT 1
\&        my $record = $bag\->select( author => \*(AqNicolas\*(Aq )\->detect( subject => \*(AqICT\*(Aq );
\&    }
\&
\&    #NOTES
\&    {
\&
\&        #This creates an iterator with a specialized SQL query:
\&
\&        #SELECT * FROM DATA WHERE author = \*(AqNicolas\*(Aq
\&        my $iterator = $bag\->select( author => \*(AqNicolas\*(Aq );
\&
\&        #But this does not
\&        my $iterator2 = $iterator\->select( title => "Hello world" );
\&
\&        #\*(Aqtitle\*(Aq does not have a corresponding table column, so it falls back to the default implementation,
\&        #and loops over every record.
\&
\&    }
\&    {
\&
\&        #this is faster..
\&        my $iterator = $bag\->select( author => \*(AqNicolas\*(Aq )\->select( title => \*(AqHello world\*(Aq);
\&
\&        #..than
\&        my $iterator2 = $bag\->select( title => \*(AqHello world\*(Aq )\->select( author => \*(AqNicolas\*(Aq );
\&
\&        #reason:
\&
\&        #   the select statement of $iterator creates a specialized query, and so reduces the amount of records to loop over.
\&        #   $iterator is a L<Catmandu::Store::DBI::Iterator>.
\&
\&        #   the select statement of $iterator2 does not have a specialized query, so it\*(Aqs a generic L<Catmandu::Iterator>.
\&        #   the second select statement of $iterator2 receives this generic object as its source, and can only loop over its records.
\&
\&    }
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
Catmandu::Store::DBI::Bag provides some method overrides specific for \s-1DBI\s0 interfaces,
to make querying more efficient.
.SH "METHODS"
.IX Header "METHODS"
.SS "store_with_table"
.IX Subsection "store_with_table"
Equivalent to the \f(CW\*(C`store\*(C'\fR accessor, but ensures that the table for this bag exists.
.ie n .SS "select($key => $val)"
.el .SS "select($key => \f(CW$val\fP)"
.IX Subsection "select($key => $val)"
Overrides equivalent method in Catmandu::Bag.
.PP
Either returns a generic Catmandu::Iterator or a more efficient Catmandu::Store::DBI::Iterator.
.PP
Expect the following behaviour:
.IP "\(bu" 4
the key has a corresponding table column configured
.Sp
a \s-1SQL\s0 where clause is created in the background:
.Sp
\&.. \s-1WHERE\s0 \f(CW$key\fR = \f(CW$val\fR
.Sp
Chained select statements with existing table columns result in a combined where clause:
.Sp
.Vb 1
\&    .. WHERE $key1 = $val1 AND $key2 = $val2 ..
.Ve
.Sp
The returned object is a Catmandu::Store::DBI::Iterator, instead of the generic Catmandu::Iterator.
.IP "\(bu" 4
the key does not have a corresponding table column configured
.Sp
The returned object is a generic Catmandu::Iterator.
.Sp
This iterator can only loop over the records provided by the previous Catmandu::Iterable.
.PP
A few important notes:
.IP "\(bu" 4
A select statement only results in a Catmandu::Store::DBI::Iterator, when it has a mapped key,
and the previous iterator is either a Catmandu::Store::DBI::Bag or a Catmandu::Store::DBI::Iterator.
.IP "\(bu" 4
As soon as the returned object is a generic Catmandu::Iterator, any following select statement
with mapped columns will not make a more efficient Catmandu::Store::DBI::Iterator.
.PP
In order to make your chained statements efficient, do the following:
.IP "\(bu" 4
create indexes on the table columns
.IP "\(bu" 4
put select statements with mapped keys in front, and those with non mapped keys at the end.
.PP
To configure table columns, see Catmandu::Store::DBI.
.ie n .SS "detect($key => $val)"
.el .SS "detect($key => \f(CW$val\fP)"
.IX Subsection "detect($key => $val)"
Overrides equivalent method in Catmandu::Bag.
.PP
Also returns first record where \f(CW$key\fR matches \f(CW$val\fR.
.PP
Works like the select method above, but adds the \s-1SQL\s0 statement '\s-1LIMIT 1\s0' to the current \s-1SQL\s0 query in the background.
.SS "\fBfirst()\fP"
.IX Subsection "first()"
Overrides equivalent method in Catmandu::Bag.
.PP
Also returns first record using the current iterator.
.PP
The parent method uses a generator, but fetches only one record.
.PP
This method adds the \s-1SQL\s0 statement '\s-1LIMIT 1\s0' to the current \s-1SQL\s0 query.
.SS "\fBcount()\fP"
.IX Subsection "count()"
Overrides equivalent method in Catmandu::Bag.
.PP
When the source is a Catmandu::Store::DBI::Bag, or a Catmandu::Store::DBI::Iterator,
a specialized \s-1SQL\s0 query is created:
.PP
.Vb 1
\&    SELECT COUNT(*) FROM TABLE WHERE (..)
.Ve
.PP
The select statement of the source is between the parenthesises.